1. Field of the Invention
This invention relates to a magnetic recording medium for use in a magnetic recording apparatus using a magnetic tape, or the like. This invention particularly relates to a thin metal film type magnetic recording medium exhibiting markedly improved corrosion resistance and durability.
2. Description of the Prior Art
Many of the conventional magnetic recording media are of the so-called coating type and made by using powdered magnetic materials such as magnetic oxide particles, for example, .gamma.-Fe.sub.2 O.sub.3, Co-doped .gamma.-Fe.sub.2 O.sub.3, Fe.sub.3 O.sub.4, Co-doped Fe.sub.3 O.sub.4, Berthollide compounds of .gamma.-Fe.sub.2 O.sub.3 and Fe.sub.3 O.sub.4, Co-doped Berthollide compounds, or CrO.sub.2, or magnetic alloy particles containing, as main constituents, Fe, Ni, Co and the like. These powdered magnetic materials are dispersed in organic binders such as vinyl chloride-vinyl acetate copolymers, styrene-butadiene copolymers, epoxy resins and polyurethane resins. The dispersions thus obtained are then applied to non-magnetic substrates and dried to form the magnetic recording media.
Recently, so-called thin metal film type magnetic recording media using no binders have attracted attention because of their ability to meet strong demand for high density recording. The magnetic recording media of this type have magnetic recording layers which consist of thin ferromagnetic metal films formed by a process such as vacuum deposition, sputtering, ion plating or plating. Thus various efforts are being made to develop thin metal film type magnetic recording media suitable for practical use.
FIGS. 1 and 2 are explanatory views schematically showing the configurations of conventional magnetic recording media. As shown in FIG. 1, the conventional magnetic recording medium comprises a non-magnetic substrate 2 and a thin ferromagnetic metal film layer 1 overlaid on the substrate 2. However, since the thin ferromagnetic metal film layer 1 normally consists of an aggregate of columnar grains 3, corrosion readily arises through the spaces between the columnar grains 3. Also, as shown in FIG. 2, it has been proposed to overlay an overcoat film 4 made of a polymer film on the thin ferromagnetic metal film layer 1. However, since the overcoat film 4 of the thin metal film type magnetic recording medium is composed of relatively large polymer molecules, the overcoat film 4 does not enter the spaces between the columnar grains 3, but instead is simply overlaid on the columnar grains 3 in a plane form. Thus the overcoat film 4 is not so strong, and pin holes are readily generated in the portions of the overcoat film 4 between the columnar grains 3. When pin holes are generated in the overcoat film 4, corrosion of the columnar grains 3 readily proceeds through the pin holes.
Further, the conventional magnetic recording medium entails an even more troublesome problem in that, when the magnetic recording medium is used as a magnetic tape and moved in a magnetic recording and reproducing apparatus, the thin ferromagnetic metal film layer of the magnetic recording medium readily wears due to contact with the magnetic head or the guide post of the apparatus.
The aforesaid drawbacks of the conventional magnetic recording medium present a very real problem with regard to reliability required for the magnetic recording medium. However, there has not heretofore been any magnetic recording medium that eliminates the aforesaid drawbacks.